Feedback-Based Configuration Of A Hybrid Fiber-Coaxial Network

ABSTRACT

Circuitry of a fiber node which is configured to couple to an optical link and an electrical link may comprise an electrical-to-optical conversion circuit for transmitting on the optical link. The circuitry may be operable to receive signals via the optical link. The circuitry may select between or among different configurations of the electrical-to-optical conversion circuit based on the signals received via the optical link. The signals received via the optical link may be intended for one or more gateways served by the fiber node or may be dedicated signals intended for configuration of the circuitry. The circuitry may be operable to generate feedback and insert the feedback into a datastream received from one or more gateways via the electrical link prior to transmitting the datastream onto the optical link.

CLAIM OF PRIORITY

This patent application is a continuation of U.S. patent applicationSer. No. 15/652,982 filed on Jul. 8, 2017, now U.S. Pat. No. 10,469,166,which is a continuation of U.S. patent application Ser. No. 15/279,653filed on Sep. 29, 2016, now U.S. Pat. No. 9,712,236, which is acontinuation of U.S. patent application Ser. No. 14/157,146 filed onJan. 16, 2014, now U.S. Pat. No. 9,461,742, which makes reference to,claims priority to and claims benefit from U.S. Provisional PatentApplication No. 61/753,156, which was filed on Jan. 16, 2013.

Each of the above identified applications is hereby incorporated hereinby reference in its entirety.

INCORPORATION BY REFERENCE

This patent application makes reference to U.S. patent application Ser.No. 14/147,628 titled “Advanced Fiber Node” and filed on Jan. 6, 2014,which is hereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

Aspects of the present application relate to communication networks.More specifically, aspects of the present application relate to a methodand system for a feedback-based configuration of a hybrid fiber-coaxialnetwork.

BACKGROUND OF THE INVENTION

Conventional systems and methods for communications can be overly powerhungry, slow, expensive, and inflexible. Further limitations anddisadvantages of conventional and traditional approaches will becomeapparent to one of skill in the art, through comparison of such systemswith some aspects of the present invention as set forth in the remainderof the present application with reference to the drawings.

BRIEF SUMMARY OF THE INVENTION

A system and method for a feedback-based configuration of a hybridfiber-coaxial network, substantially as shown in and/or described inconnection with at least one of the figures, as set forth morecompletely in the claims.

Advantages, aspects and novel features of the present disclosure, aswell as details of various implementations thereof, will be more fullyunderstood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram depicting an example hybrid fiber-coaxial (HFC)network.

FIG. 2A is a diagram depicting an example implementation of a fibernode.

FIG. 2B depicts an example implementation of a reconfigurable fibernode.

FIG. 3 is a diagram depicting an example implementation of anoptical-to-electrical (O/E) conversion circuit in a fiber node.

FIG. 4 is a diagram depicting an example implementation of anelectrical-to-optical (E/O) conversion circuit in a fiber node.

FIG. 5 is a diagram depicting example components of a headend.

FIG. 6 is a flow chart illustrating example steps for a configuration ofa fiber node and headend.

FIG. 7 is a flow chart illustrating example steps for a configuration ofa fiber node and headend.

FIG. 8 illustrates characteristics of an example optical component.

DETAILED DESCRIPTION OF THE INVENTION

As utilized herein the terms “circuits” and “circuitry” refer tophysical electronic components (i.e. hardware) and any software and/orfirmware (“code”) which may configure the hardware, be executed by thehardware, and or otherwise be associated with the hardware. As usedherein, for example, a particular processor and memory may comprise afirst “circuit” when executing a first one or more lines of code and maycomprise a second “circuit” when executing a second one or more lines ofcode. As utilized herein, “and/or” means any one or more of the items inthe list joined by “and/or”. As an example, “x and/or y” means anyelement of the three-element set {(x), (y), (x, y)}. As another example,“x, y, and/or z” means any element of the seven-element set {(x), (y),(z), (x, y), (x, z), (y, z), (x, y, z)}. As utilized herein, the term“exemplary” means serving as a non-limiting example, instance, orillustration. As utilized herein, the terms “e.g.,” and “for example”set off lists of one or more non-limiting examples, instances, orillustrations. As utilized herein, circuitry is “operable” to perform afunction whenever the circuitry comprises the necessary hardware andcode (if any is necessary) to perform the function, regardless ofwhether performance of the function is disabled, or not enabled, by someuser-configurable setting.

FIG. 1 is a diagram depicting an example hybrid fiber-coaxial (HFC)network. The example HFC network 100 comprises a headend 102, a fibernode 104, amplifiers 106 ₁-106 ₃, splitters 110 ₁-110 ₄, and gateways112 ₁-112 ₅.

The headend 102 comprises a cable modem termination system (CMTS) forhandling DOCSIS traffic to and from the cable modems of gateways 112₁-112 ₅ and one or more modulators (e.g., one or more “edge QAMs”) forhandling downstream multimedia traffic to the audio/video receivers ofthe gateways 112 ₁-112 ₅.

The fiber node (FN) 104 may provide an interface between the opticalnetwork 120 and the electrical network 130. The fiber node 104 may, forexample, be as described below with reference to FIGS. 2A-6.

Each of the amplifiers 106 ₁-106 ₃ comprises a bidirectional amplifierwhich may amplify downstream signals and upstream signals, wheredownstream signals are input via upstream interface 107 a and output viadownstream interface 107 b, and upstream signals are input viadownstream interface 107 b and output via upstream interface 107 a. Theamplifier 106 ₁, which amplifies signals along the main coaxial “trunk,”may be referred to as a “trunk amplifier.” The amplifiers 106 ₂ and 106₃, which amplify signals along “branches” split off from the trunk, maybe referred to as “branch” or “distribution” amplifiers.

Each of the splitters 110 ₁-110 ₄ comprises circuitry operable to outputsignals incident on each of its interfaces onto each of its otherinterfaces. Each of the splitters 110 ₁-110 ₄ may be a passive or activedevice.

Each of the gateways 112 ₁-112 ₅ may comprise cable modem circuitryoperable to communicate with, and be managed by, the headend 102 inaccordance with one or more standards (e.g., DOCSIS). Each of thegateways 112 ₁-112 ₅ may comprise one or more audio/video receiversoperable to receive multimedia content (e.g., in the form of one or moreMPEG streams) transmitted by the headend 102 in accordance with one ormore standards used for cable television. Each of the gateways 112 ₁-112₅ may reside at the premises of a cable/DOCSIS subscriber.

FIG. 2A is a diagram depicting an example implementation of a fibernode. Referring to FIG. 2A, the depicted example implementation of fibernode 104 comprises a wave division multiplexer (WDM) 204, anelectro-mechanical aligner 206, and modules 202 ₁-202 _(N) (where N isan integer).

The WDM 204 is operable to multiplex up to N (an integer) upstreamsignals from up to N modules 202 onto the fiber 103, and demultiplex upto N downstream signals from the fiber 103 to up to N modules 202. Forrelatively low values of N and/or relatively low amounts of usablebandwidth on fiber 103, the multiplexing may be referred to as “coarsewave division multiplexing.” For relatively high values of N and/orrelatively high amounts of usable bandwidth on fiber 103, themultiplexing may be referred to as “dense wave division multiplexing.”

The aligner 206 may be operable to mechanically adjust the position ofthe fiber 103, the WDM 204, each of the modules 202 ₁-202 _(N), anoptical detector of each of the modules 202 ₁-202 _(N), and/or a laserdiode of each of the modules 202 ₁-202 _(N) in response to an electricalcontrol signal from one or more of the modules 202 ₁-202 _(N). In thismanner, after the fiber node 104 has been deployed in the HFC network,and is in operation serving gateways 112 ₁-112 ₅, alignment of theoptical components of the fiber node 104 may be adjusted via, forexample, dedicated control signals sent from the headend 102, and/orautonomously based on monitoring in the fiber node 104.

Each module 202 _(n) (1≤n≤N) is operable to receive an optical signalvia fiber 103 and output a corresponding electrical signal on coaxialcable 105 _(n), and receive an electrical signal on coaxial cable 105_(n) and output a corresponding optical signal on fiber 103. Each module202 _(n) may, for example, be as described below with reference to FIGS.2B-6.

FIG. 2B depicts an example implementation of a reconfigurable fibernode. Referring to FIG. 2B, there is shown a module 202 _(n) (1≤n≤N) ofthe fiber node (FN) 104. The example module 202 _(n) comprises adownstream optical-to-electrical (O/E) conversion circuit 212, anupstream electrical-to-optical (E/O) conversion circuit 210, adownstream receiver 214, a downstream modulator 216, an upstream burstreceiver 206, an upstream encoder 208, a diplexer 222 and aconfiguration controller 218.

The O/E conversion circuit 212 is operable to convert the optical signal248 to an electrical signal (voltage and/or current on a conductor) 242.

Referring briefly to FIG. 3, an example implementation of the O/Econversion circuit 212 comprises an optical detector 302, an automaticgain control (AGC) circuit 304, a temperature controller 306, test andmeasurement circuitry 310, and control logic 308. The optical detector302 is operable to output an electrical signal 322 having a currentand/or voltage that corresponds to the intensity of the optical signal248. The automatic gain control (AGC) circuit 304 operates to controlthe current and/or voltage levels of signal 322 to output a signal 242that remains between desired levels. The control logic 308 is operableto control the various components of the O/E conversion circuit 212 andto interface the O/E conversion circuit 212 to the configurationcontroller 218. The temperature controller 306 is operable to heatand/or cool the optical detector 302 to maintain the optical detector302 within a desired range of temperatures. The temperature controller306 may perform heating, passive cooling (i.e., heatsinking that doesnot require input power), and/or active cooling (e.g., MEMS heatsinksfans, heat exchangers, or refrigerators that require input power). Thecenter wavelength of the detector 302 (the wavelength for which powercoupling between the optical signal and the electrical signal is best)may depend on the temperature of the detector 302. Accordingly, thetemperature controller 306 may control the temperature of the detector302 to maintain a particular center wavelength and/or to switch betweendifferent center wavelengths. For example, the temperature may becontrolled to track λ1 and/or may be controlled to switch from λ1 to λ2.

Returning to FIG. 2B, the O/E conversion circuit 212 may output amonitor signal 250 which may provide information about operation and/orconfiguration of the O/E conversion circuit 212. The signal 250 maycomprise measurement/calibration data and/or configuration settings forthe O/E conversion circuit 212. The signal 250 may convey, for example,measured wavelength of a received optical signal, measured intensity ofthe received optical signal, measured temperature of the detector 302,and/or any other characteristics of the O/E conversion circuit 212 whichmay be useful for configuring the module 202 _(n) and/or for providingfeedback to the headend 102. The O/E conversion circuit 212 may beconfigured via control signal 240 from configuration controller 218.

The receiver 214 may be operable to process the electrical signal 242 torecover data which is then output as signal 244. Such processing mayinclude, for example, equalization, filtering, demapping, decoding,deinterleaving, and/or the like. Any of the functions of the receiver214 may be configured via control signal 213. The receiver 214 mayoutput a monitor signal 215.

The signal 215 may comprise downstream data from the headend 102intended for one or more gateways 112 and “sniffed” by the module 202_(n), and/or may comprise performance metrics (symbol error rate, a biterror rate, amount of multimode dispersion, signal-to-noise ratio,and/or the like) of signal(s) 242 and/or 244 measured by the receiver214. In this manner, after the module 202 _(n) has been deployed in theHFC network and is in operation serving gateways 112, the module 202_(n) may autonomously configure itself without requiring interventionfrom the service provider. Additionally or alternatively, the signal 215may comprise dedicated control data from the headend 102 intended forthe module 202 _(n). In this manner, after the module 202 _(n) has beendeployed in the HFC network and is in operation serving gateways 112, aservice provider may intervene to reconfigure the module 202 _(n) butcan do so from a remote location without having to physically send atechnician to the FN 104.

Referring briefly to FIG. 4, an example implementation of the E/Oconversion circuit 210 comprises a laser diode 402, a driver/AGC circuit404, a temperature controller 406, test and measurement circuitry 410,and control logic 408. The laser diode 402 is operable to output anoptical signal 246 whose intensity corresponds to the voltage and/orcurrent of the electrical signal 422. The driver/AGC circuit 404operates to control the current and/or voltage levels of signal 230 tooutput a signal 422 that remains between desired levels. The controllogic 408 is operable to control the various components of the E/Oconversion circuit 210 and to interface the E/O conversion circuit 210to the configuration controller 218. The temperature controller 406 isoperable to heat and/or cool the laser diode 402 to maintain the laserdiode 402 within a desired range of temperatures. The temperaturecontroller 406 may perform heating, passive cooling (i.e., heatsinkingthat does not require input power), and/or active cooling (e.g., MEMSheatsinks fans, heat exchangers, or refrigerators that require inputpower). The center wavelength of optical signal transmitted by the laserdiode 402 may depend on the temperature of the laser diode 402.Accordingly, the temperature controller 406 may control the temperatureof the laser diode 402 to maintain a particular center wavelength and/orto switch between different center wavelengths. For example, thetemperature may be controlled to track λ1 and/or may be controlled toswitch from λ1 to λ2.

The modulator 216 may be operable to modulate the signal 244 and/or 217onto one or more RF carriers to generate the signal 238 which istransmitted onto the coax 105 _(n) via the diplexer 222. The signal 217may comprise feedback and/or other control information that is insertedinto/merged with the data 244 for communication to the gateways 112served via coax 105 _(n). The modulation may include, for example,interleaving, filtering, bit-to-symbol mapping, encoding, upconverting,and/or other functions. Any of the functions of the modulator 216 may beconfigured via control signal 219. The modulation performed by modulator216 may be in accordance with one or more DOCSIS standard (e.g., DOCSIS1.0, 2.0, 3.0, etc.) cable television standard, and/or other standardsupported by the gateways 112 served via coax 105 _(n).

The diplexer 222 may be operable to couple downstream signal 238 ontothe coaxial cable 105 _(n) while concurrently passing upstream signals(originating from gateways 112 served via coax 105 _(n)) from coax 105_(n) into the FN as signal 236.

The receiver 206 is operable to process the electrical signal 236 torecover data which is then output as signal 232. Such processing mayinclude, for example, equalization, filtering, demapping, decoding,deinterleaving, and/or the like. Any of the functions of the receiver206 may be configured via control signal 221. The receiver 206 mayoutput a monitor signal 207.

The signal 207 may comprise upstream data from the gateway(s) 112intended for the headend 102 and “sniffed” by the module 202 _(n) and/orthe signal 207 may comprise performance metrics (SER, BER, SNR, and/orthe like) measured by the receiver 206. In this manner, after the module202 _(n) has been deployed in the HFC network and is in operationserving gateways 112, the module 202 _(n) may autonomously configureitself without requiring intervention from the service provider.Additionally or alternatively, the signal 207 may comprise dedicatedcontrol data from the gateway(s) 112 intended for the module 202 _(n).In this manner, after the module 202 _(n) has been deployed in the HFCnetwork and is in operation serving gateways 112, a service provider mayintervene to reconfigure the module 202 n but can do so from a remotelocation without having to physically send a technician to the FN 104.

The modulator 208 is operable to modulate the signal 232 and/or 209 ontoone or more RF carriers to generate the signal 230. The signal 209 maycomprise feedback and/or other control information that is insertedinto/merged with the data 232 for communication to the headend 102 thatserves the module 202 _(n). The modulation may include, for example,interleaving, filtering, bit-to-symbol mapping, encoding, upconverting,and/or other functions. Any of the functions of the modulator 208 may beconfigured via control signal 211. The modulation performed by modulator208 may be in accordance with one or more DOCSIS standards (e.g., DOCSIS1.0, 2.0, 3.0, etc.), Ethernet over Passive Optical Network (EPON),and/or other standard supported by the headend 102.

The E/O conversion circuit 210 may comprise, for example, a laser diodeand a gain control circuit for converting an electrical signal to anoptical signal.

Returning to FIG. 2B, the E/O conversion circuit 210 may output amonitor signal 252 which may provide information about operation and/orconfiguration of the O/E conversion circuit 210. The signal 252 maycomprise measurement/calibration data and/or configuration settings forthe E/O conversion circuit 210. The signal 252 may convey, for example,measured wavelength of a transmitted optical signal, measured intensityof the transmitted optical signal, measured temperature of the laserdiode 402, and/or any other characteristics of the E/O conversioncircuit 210 which may be useful for configuring the module 202 _(n)and/or for providing feedback to the headend 102. The O/E conversioncircuit 212 may be configured via control signal 234 from configurationcontroller 218.

The configuration controller 218 may be operable to controlconfiguration of the module 202 _(n), send feedback and/or othercontrols signals to the headend 102, and/or send feedback and/or othercontrol signals to the gateways 112 served via coax 105 _(n). Theconfiguration of the various components of module 202 _(n) may beachieved via signals 240, 213, 219, 221, 211, and 234. The configurationand/or control signals generated by controller 218 may be based on anyone or more of signals 215, 207, 250, and 252 described above.

FIG. 5 is a diagram depicting example components of a headend. Shown area WDM 524, optical detectors 504 ₁ and 504 ₂, laser diodes 506 ₁ and 506₂, and a memory 502.

Each of the optical detectors 504 ₁ and 504 ₂ may be similar to thedetector 302 described above. Each of the laser diodes 506 ₁ and 506 ₂may be similar to the laser diode 402 described above.

Each of the detectors in the headend 102 and the fiber node 104 may havea nominal center wavelength (the wavelength that the detector detectsbest at a particular temperature) which, due to non-idealities, may bedifferent than the nominal center wavelength of any one or more othersof the detectors. Similarly, each of the laser diodes in the headend 102and the fiber node 104 may have a nominal center wavelength (thewavelength of peak intensity) which, (due to non-idealities, may bedifferent than the nominal center wavelength of any one or more othersof the laser diodes.

The nominal center frequency of various detectors and diodes may betaken into account when building the headend 102 and when building thefiber node 104. For example, when a diode 402 and detector 302 for aparticular module 202 _(n) are selected, a diode and detector havingsufficiently different nominal center wavelengths may be chosen.Similarly, when N diodes 506 [or detectors 504] to be placed in theheadend 102 or in N modules 202 intended for FN 104 are selected, Nlaser diodes [or detectors] with particular and/or sufficientlydifferent nominal center wavelengths may be chosen. In this regard,during manufacturing, laser diodes and detectors may be categorized or“binned” based on their nominal center wavelengths. A plurality of laserdiodes and detectors having nominal center wavelengths that span therange of wavelengths supported by the WDMs 204 and 524 may then beinstalled into each headend 102 and/or fiber node 104.

The nominal center frequency of various detectors and diodes may betaken into account when which modules 202 ₁-202 _(n) to be installed inthe fiber node 104 is determined. For example, given the nominal centerwavelengths of the laser diode 506 ₁ and detector 504 ₁ of the headend,it may be desirable to select as module 202 ₁ a module 202 whosedetector 302 has a nominal center frequency very close to the nominalcenter frequency of laser diode 504 ₁ and whose laser diode 402 has anominal center frequency very close to the nominal center frequency oflaser diode 506 ₁.

The nominal center frequency of various detectors and diodes may betaken into account when the headend 102 and/or the installed modules 202₁-202 _(N) are configured. For example, assuming two modules 202 ₁ and202 ₂ are installed in the fiber node 104, the modules 202 ₁ and 202 ₂may measure and transmit their respective diode and detector nominalcenter wavelengths as feedback/control information, which the headend102 may then store in memory 502. For example, the nominal centerwavelength of the laser diode 402 in module 202 ₁ may be longer than thenominal center wavelength of the laser diode 402 in module 202 ₂. Theheadend 102 may then assign the module 202 ₁ to a longer upstreamwavelength, pair module 202 ₁ with the one of detectors 504 ₁ and 504 ₂having a nominal center frequency closer to that longer wavelength,assign the module 202 ₂ to a shorter upstream wavelength, and pairmodule 202 ₁ with the one of detectors 504 ₁ and 504 ₂ having a nominalcenter frequency closer to that longer wavelength. The result may bethat less power is consumed in trying to stabilize the wavelength of thediodes, since they are allowed to operate close to their nominal centerwavelength.

As a result, characterizing nominal center wavelengths and using suchinformation in building, installing, and configuring the headend 102 andfiber node 104, less margin may be needed to allow for drift ormismatch. This may enable transmitting more bits per wavelength and/ormore wavelengths per fiber 103 _(n).

FIG. 6 is a flow chart illustrating example steps for a configuration ofa fiber node and headend. The process begins in block 602 with theheadend 102 transmitting a downstream optical signal onto fiber 103. Inblock 604, the fiber node 104 receives the downstream optical signal andattempts to optimize one or more performance metrics by adjustingalignment via the aligner 206 and/or adjusting temperature viatemperature controller 406 in a closed-loop fashion. This may be donefor each module 202 of the fiber node 104 and for each center wavelengthof the downstream optical signal to find the best configuration of thefiber node 104. Adjustment of the optical components may be instead of,or in addition to, adjustment of the electrical components such as AGC304 and receiver 214. In block 606, if an acceptable level of theperformance metric cannot be achieved for each module 202 of the fibernode 104, feedback (e.g., measured characteristics of the optical signaland/or the measured values of the performance metric for one or more ofthe modules 202 ₁-202 _(N)) is sent to the headend 102. In block 610,the headend 102 uses the feedback to adjust its laser diode(s) to finetune the center wavelengths being sent on fiber 103, to coarsely selectone or more different center wavelengths to send on the fiber 103,and/to adjust an output power of its laser diode(s).

FIG. 7 is a flow chart illustrating example steps for a configuration ofa fiber node and headend. The process begins in block 702 with the fibernode 104 transmitting an optical signal onto fiber 103. In block 704,the headend 102 receives the optical signal and attempts to optimize oneor more performance metrics by adjusting alignment (e.g., via an alignersuch as aligner 206 implemented in the headend 102) and/or adjustingwavelength (e.g., via a temperature controller such as temperaturecontroller 406 implemented in the headend 102) in a closed-loop fashion.This may be done for each center wavelength of the upstream opticalsignal to find the best configuration of the fiber node 104. Adjustmentof the optical components may be instead of, or in addition to,adjustment of the electrical components in the headend 102. In block706, if an acceptable level of the performance metric cannot be achievedfor each module 202 of the fiber node 104, feedback (e.g., measuredcharacteristics of the optical signal and/or the measured values of theperformance metric for one or more of the center wavelengths) is sent tothe fiber node 104. In block 710, the fiber node 104 uses the feedbackto finely tune one or more center wavelengths (e.g., via temperaturecontroller(s) 406), to adjust alignment of the optical components (e.g.,via the aligner 206), and/or adjust output power of one or more of itslaser diodes 402 (e.g., via AGC 404).

FIG. 8 illustrates characteristics of an example optical component.Shown is the bandwidth of an example optical component such as detector302 or laser 402. The component has a nominal center wavelength λ1 asindicated by the solid line. When the component heats up (relative thetemperature at which its nominal center wavelength was measured) itscenter wavelength moves to λ1⁺ and when it cools down (relative thetemperature at which its nominal center wavelength was measured) itscenter wavelength moves to λ1⁻.

In an example implementation of this disclosure, circuitry (e.g.,circuitry of module 202 _(n)) for use in a fiber node (e.g., 104) may beconfigured to couple to an optical link (e.g. 103) and to an electricallink (e.g., 105 _(n)). The circuitry may comprise anelectrical-to-optical conversion circuit (210) for transmitting on theoptical link. The circuitry may be operable to select among differentconfigurations of the electrical-to-optical conversion circuit based onsignals (e.g., 248) received via the optical link. The signals receivedvia the optical link may be intended for one or more gateways served bythe fiber node (i.e., the circuitry may “sniff” them) and/or may beintended for the fiber node and dedicated for configuration of thecircuitry. In one configuration, the electrical-to-optical conversioncircuit may transmit at a first power onto the optical link, and inanother configuration may transmit at a second power, higher than thefirst power, onto the optical link. In one configuration, theelectrical-to-optical conversion circuit may transmit at a firstwavelength onto the optical link, and in another configuration it maytransmit at a second wavelength, shorter than the first wavelength, ontothe optical link. The circuitry may be operable to generate feedbackdata and insert the feedback data into a datastream received from one ormore gateways via the electrical link prior to transmitting thedatastream onto the optical link.

The electrical-to-optical conversion circuit may comprise a laser diode(e.g., 402) and a temperature controller (e.g., 406) operable to performactive cooling. In one configuration, the temperature controller may beconfigured to hold the laser diode at a first temperature (which maycorrespond to the diode having a first center wavelength), and inanother configuration, the temperature controller may be configured tohold the laser diode at a second temperature, lower than the firsttemperature (which may correspond to the diode having a second centerwavelength). The fiber node may comprise a wave division multiplexer(e.g., 204) and an electro-mechanical aligner (e.g., 206) operable toadjust alignment of the laser diode and the wave division multiplexer.In one configuration, the electro-mechanical aligner may be configuredsuch that the laser diode and the wave division multiplexer are in afirst spatial arrangement (e.g., one is too far up, down, left, or righthigh relative to the other such that the optical path is misaligned),and in another configuration, the electro-mechanical aligner isconfigured such that the laser diode and the wave division multiplexerare in a second spatial arrangement (e.g., the misalignment of theoptical path is corrected).

The circuitry may comprise a first laser diode having a first nominalcenter wavelength and a second laser diode having a second nominalcenter wavelength, shorter than the first nominal center wavelength. Thecircuitry may be operable to transmit a value (e.g., a binary number)representing the first nominal center wavelength and the second nominalcenter wavelength onto the optical link for use by the headend. Thecircuitry may be configured to perform the selection among differentconfigurations of the electrical-to-optical conversion circuitautonomously based on a measured performance metric of the signalsreceived via the optical link.

Other embodiments of the invention may provide a non-transitory computerreadable medium and/or storage medium, and/or a non-transitory machinereadable medium and/or storage medium, having stored thereon, a machinecode and/or a computer program having at least one code sectionexecutable by a machine and/or a computer, thereby causing the machineand/or computer to perform the methods described herein.

Accordingly, the present invention may be realized in hardware,software, or a combination of hardware and software. The presentinvention may be realized in a centralized fashion in at least onecomputing system, or in a distributed fashion where different elementsare spread across several interconnected computing systems. Any kind ofcomputing system or other apparatus adapted for carrying out the methodsdescribed herein is suited. A typical combination of hardware andsoftware may be a general-purpose computing system with a program orother code that, when being loaded and executed, controls the computingsystem such that it carries out the methods described herein. Anothertypical implementation may comprise an application specific integratedcircuit or chip.

The present invention may also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which when loaded in a computer systemis able to carry out these methods. Computer program in the presentcontext means any expression, in any language, code or notation, of aset of instructions intended to cause a system having an informationprocessing capability to perform a particular function either directlyor after either or both of the following: a) conversion to anotherlanguage, code or notation; b) reproduction in a different materialform.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

What is claimed is:
 1. A system comprising: circuitry for use in a fibernode configured to couple to an optical link and to an electrical link,wherein: said circuitry comprises an electrical-to-optical conversioncircuit for transmission on said optical link; said circuitry comprisesa first laser diode having a first operating wavelength and a secondlaser diode having a second operating wavelength, shorter than saidfirst operating wavelength; and said circuitry is operable to transmitat least one signal identifying said first operating wavelength and saidsecond operating wavelength onto said optical link for use by a headendthat serves said fiber node.